This disclosure relates to abradable coatings for rotatable blades. Abradable seals or coatings (rub coatings) can be used to protect moving parts from damage during rub interaction while providing a small clearance. Such seals are used in turbomachines to interface with abrasive tips of a rotating blade stage.
The abrasive tips include coatings to enhance performance and limit heat generation and heat transfer to the blade. The abrasive tips, upon rubbing the abradable seal, remove portions of the abradable seal. The portions of the abradable seal can transfer to the abrasive tips and adhere to the abrasive tips. Carbonized portions of the abradable seal that adhere to the abrasive tips can build up. The portions of the carbon based materials that build up between the grit particles of the abrasive tip (i.e. clogging) can cause frictional heating during rub events. The frictional heating can affect the polyurethane erosion resistant coating on the gas path surfaces of the blade. Thus, the very problem that the abrasive blade tip is designed to prevent, instead occurs through a different mechanism. Pending U.S. non-provisional application no. US 2015/0233255 is incorporated herein by reference.
What is needed is an abradable coating that prevents clogging of the abrasive tip due to build-up of carbonized rub debris.